CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Millions	Total	Preferred Stock	Common Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Treasury Stock
Beginning balance at Dec. 31, 2017	$ 48,730	$ 0	$ 7	$ 31,656	$ 30,700	$ (926)	$ (12,707)
Beginning balance (shares) at Dec. 31, 2017		4,475,000	661,724,927
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effects from adoption of new lease standard	0				201	(201)
Comprehensive income (loss)	874				1,346	(472)
Common Stock Dividends, Shares			22,467
Dividends, Common Stock	(197)		$ 0		(199)
Dividends, Share-based Compensation, Stock				2
Cash dividends - preferred series	(52)				(52)
Purchases of treasury stock	(273)						(273)
Issuances of common stock and restricted stock, shares, net of forfeitures			2,452,786
Issuances of common stock and restricted stock, value, net of forfeitures	49		$ 0	49
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, shares			675,871
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, value	14		$ 0	14
Compensation expense for restricted stock units and stock options	58			58
Ending balance at Mar. 31, 2018	49,203	$ 0	$ 7	31,779	31,996	(1,599)	(12,980)
Ending balance (shares) at Mar. 31, 2018		4,475,000	664,876,051
Beginning balance at Dec. 31, 2018	51,668	$ 0	$ 7	32,040	35,875	(1,263)	(14,991)
Beginning balance (shares) at Dec. 31, 2018		4,475,000	667,969,069
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative effects from adoption of new lease standard	(11)				(11)
Comprehensive income (loss)	2,015				1,412	603
Common Stock Dividends, Shares			32,700
Dividends, Common Stock	(191)		$ 0		(194)
Dividends, Share-based Compensation, Stock				3
Cash dividends - preferred series	(52)				(52)
Purchases of treasury stock	(65)						(65)
Issuances of common stock and restricted stock, shares, net of forfeitures			2,641,635
Issuances of common stock and restricted stock, value, net of forfeitures	52		$ 0	52
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, shares			5,000
Exercise of stock options and warrants, tax effects of exercises and restricted stock vesting, value	0		$ 0	0
Compensation expense for restricted stock units and stock options	65			65
Ending balance at Mar. 31, 2019	$ 53,481	$ 0	$ 7	$ 32,160	$ 37,030	$ (660)	$ (15,056)
Ending balance (shares) at Mar. 31, 2019		4,475,000	670,648,404